Suppression of coke and heavy hydrocarbon formation in hydrocarbon units

ABSTRACT

Coke formation and deposits in thermal and catalytic hydrocarbon cracking units and catalytic dehydrogenation units are suppressed by introducing an aqueous solution of an alkali metal salt or hydroxide into the hydrocarbon flow at a point downstream of the furnace zone of the unit.

United States Patent 1 3,617,479

[72] Inventors James Ely Klng,.lr. [5|] lnt.Cl Clog 9/16,

Groves; C07c 11/06, C070 5/18 Sidney Theodore Jones, Port Neches, both [50] Field of Search 208/48; of Tex. 260/683, 680 R [2 I] Appl. No. 56,486 221 Filed July 20, 1970 1 References Cited [45] Patented Nov. 2, 1971 UNITED STATES PATENTS 1 Assignee Jefferson Chemical p y. 2,893,941 7/1959 Kohfeldt 208/48 Houston, Tex. Contlnuation-In-part of application Ser. No. g g g i' ixg s .rsls an .rammern 872,220 on. 1969 now abandoned. Attorneys-John R. Kirk, Jr. and H. G. Jackson [54] SUPPRESSION 0F COKE AND HEAVY ABSTRACT: Coke formation and deposits in thermal and HYDROCARBON FORMATION IN HYDROCARBON UNITS catalytrc hydrocarbon cracking un ts and catalytic 9 Claims 2 Drum a dehydrogenation umts are suppressed by introducing an aquea ous solution of an alkali metal salt or hydroxide into the [52] [1.8. CI 208/48 AA, hydrocarbon flow at a point downstream of the furnace zone 260/680 R, 260/683 R ofthe unit.

PATENTEDNBV 2 \sn 7, 479

FIG

JAMES E K'NG' SIDNEYT.JONES.

BY f

ATTORNEY,

SUPPRESSION OF COKE AND HEAVY IIYDROCARBON FORMATION IN I'IYDROCARBON UNITS CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our copending application Ser. No. 872,220 filed Oct. 29, 1969, now abandoned BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is a method for prolonging the cycle time between shutdowns of thermal and catalytic hydrocarbon cracking units and catalytic dehydrogenation units by preventing the formation of coke deposits and heavy oil and hydrocarbon polymer in the units. Specifically, this invention is a method for decreasing coke buildup and preventing heavy oil, aromatic distillate and hydrocarbon polymer formation in a hydrocarbon unit by introducing an aqueous solution of alkali metal salt or hydroxide into the unit at a point downstream of the furnace zone.

2. Description of the Prior Art Kohfeldts U.S. Pat. No. 2,893,941 (i959) discloses a process for treating liquid hydrocarbons such as heavy naphtha, kerosene, and gas oil which involves the steps of thermally cracking the hydrocarbon in the presence of potassium carbonate and steam wherein the potassium carbonate is added as an aqueous solution preferably at a point upstream from' the thermal-cracking zone to avoid the formation of coke in the cracking furnace. The preferred Kohfeldt teaching was followed by adding an aqueous potassium carbonate solution to a thermal-cracking unit for lower alkanes at a point upstream of the cracking zone and the unit became plugged with coke formation at the inline heat exchanger within 7 days. The average operating time for units with no decoking solution present is about 7 to days.

We have found that by adding an aqueous potassium carbonate solution to a hydrocarbon cracking unit at a point downstream of the cracking zone, the unit can operate without plugging due to coke for as long as 120 days and heavy oil formation decreases 10.1 percent, aromatic distillates decrease 26.3 percent and hydrocarbon polymers decrease l0.| percent. Comparable improvements are shown using other alkali metal salts or hydroxides of our invention and in cracking units for other hydrocarbon feeds, for example, crude oil, field condensate, gas oil, kerosene, naphtha, butane and natural gasoline and in dehydrogenation units for preparing butadiene from butane or butylene.

SUMMARY OF THE INVENTION The invention is an improvement in thermal and catalytic hydrocarbon cracking processes and catalytic dehydrogenation processes and comprises introducing an aqueous solution of alkali metal salt which yields an alkaline product on hydrolysis or an alkali metal hydroxide into the hydrocarbon flow at a point downstream of the furnace zone of the process to suppress the formation of coke, heavy oil, aromatic distillate and hydrocarbon polymer.

DESCRIPTION OF THE DRAWING The invention will be further illustrated with reference to the accompanying drawings which are not limitative of the invention. in FIGS. 1 and 2, a feed gas is introduced by means of line 1 into a hydrocarbon heater 2 where the gas is heated at a temperature above l,400 F. The effluent gases, at a temperature about 1.530 F., pass from the heater 2 by means ofline 3 to the quenching apparatus 4. Sufficient water to cool the gases to l,000 l ,400 F. is introduced at the top of quenching apparatus 4 in a fine spray by means of line 5 or alternatively by line 3. The addition of an alkali metal salt or hydroxide to the prequench water successfully suppresses the formation of heavy hydrocarbon and prevents coke and polymer formation in the transfer line 6 which feeds the gases to the heat exchanger 7 where they are cooled from the tem-. perature of l,000-l,400 F. to a temperature of 400-l,000 F. Quenching apparatus 4 can contain a baffle 10 against which the quenched gases impinge. In the exchanger, the heat removed from the gases is used to generate steam, which may then be used in other plant operations. These cooled gases then pass from heat exchanger 7 by means of line 8 to a quench tower which forms no part of the present invention. Beneath quenching apparatus 4, there can be located a coke collecting vessel 9 which is shown in FIG. 1 as an integral part of the quenching apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the production of olefinic hydrocarbons such as ethylene, propylene, butadiene and other cracked or dehydrogenated products by thermal or catalytic cracking of gaseous and vaporizable liquid hydrocarbons, for example, crude oil, field condensate, gas oil, kerosene, naphtha, ethane. propane, butane, and natural gasoline or catalytic dehydrogenation of butylene and butane to butadiene in a tubular pyrolysis furnace at high temperatures in the presence of steam and using short residence time, which is followed by immediate cooling or quenching of the cracked or dehydrogenated effluent; coke deposits, heavy oil, hydrocarbon polymer and aromatic distillate often form at critical points in the apparatus. The formations are serious economic problems and cause an interruption of onstream time. We have discovered that an aqueous solution of an alkali metal salt which yields an alkaline product on hydrolysis or an alkali metal hydroxide, for example, potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, lithium carbonate, barium carbonate, potassium hydroxide, sodium hydroxide, magnesium hydroxide, barium hydroxide or lithium hydroxide injected in small quantities into the hydrocarbon flow path of prequenching and subsequent cooling apparatus suppresses the formation of coke and the heavy hydrocarbons downstream from the furnace zone. Aqueous solutions of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium hydroxide or potassium hydroxide are preferred in the practice of our invention. By adding an aqueous solution of alkali metal carbonate downstream from the cracking zone or dehydrogenation zone, i.e., in the cooling or quenching apparatus including the quench pots, the quench boilers, the transfer line exchangers or connecting piping in the cracked hydrocarbon flow path, coke and heavy hydrocarbon fonnations have been reduced significantly. The quench water is cleaner and less oils are formed when our improvement is used, illustrating a reduction in secondary reactions which thereby abates water pollution because of the reduction of total carbon going into the quench water. By reducing the amount of carbon added to the quench water, less oxygen is removed from the receiving water bodies which are, for example, lakes and rivers. The determination of the amount of total carbon in the quench water is determined by the Beckman carbonaceous Analyzer and shows a 28 percent reduction in organic carbon in the water.

The salts or hydroxides may be introduced into the unit in a proportion of l to 1,000 parts per million (p.p.m.) of the hydrocarbon feed to the furnace. The preferred range of carbonate is about 10-50 ppm. of the hydrocarbon feed.

To illustrate the improvement of our invention, a testcracking furnace for cracking lower alkanes comprised of a thermal-cracking zone, a quenching apparatus and an inline heat exchanger arranged in series such that the gaseous effluent from the cracking zone flows through the quenching apparatus and then through the exchanger was put on stream. after decoking, under normal-operating conditions and an aqueous solution of potassium carbonate, 25 to 30 p.p.m. based on hydrocarbon feed, was continuously injected into the quench pot via the quench water nozzle. After 62 days of operation, the unit was shut down for inspection and repairs. Inspection revealed less coke fouling than normally found after only a few days operation with no potassium carbonate treatment. A similar furnace run was made for cracking lower alkanes wherein an aqueous solution of sodium carbonate, to p.p.m. based on hydrocarbon feed, was continuously injected into the quench pot via the quench water nozzle. After days of operation. the unit was still running with no indication of the coke buildup in the inline heat exchanger. A further similar furnace run was made for cracking lower alkanes wherein an aqueous solution of potassium hydroxide, 25 to 30 p.p.m. based on hydrocarbon feed, was continuously injected into the quench pot via the quench water nozzle. After 35 days of operation, the unit was still running with no indication of coke buildup in the inline heat exchanger. Comparable results are obtained using other salts or hydroxides of our invention in cracking units for other hydrocarbon feeds, for example, crude oil, field condensate, gas oil, kerosene, naphtha, butane and natural gasoline and in dehydrogenation units for preparing butadiene from butane or butylene.

To further illustrate the improvement of our invention, testcracking furnaces for cracking lower alkanes were operated under normal conditions while an aqueous solution of potassium carbonate, 25 to 30 p.p.m. based on the hydrocarbon feed, was continuously injected into the quench pots via the quench water nozzles for a period of 3 months. The formation of heavy oils, hydrocarbon polymer and aromatic distillate was l GaL/M. lbs. CzH

measured and compared to the same formation accumulated in 3 months in a unit where no potassium carbonate was used. The data in the following table illustrate the decrease in heavy hydrocarbon production when our improvement is used. Even though the aromatic distillate decreases when our process is used, better quality products in the aromatic distillate are obtained.

We claim:

1. ln thermal and catalytic hydrocarbon cracking processes and catalytic dehydrogenation processes, the improvement which comprises introducing an aqueous solution of alkali metal salt which yields an alkaline product on hydrolysis or an alkali metal hydroxide into the hydrocarbon flow at a point downstream of the furnace zone of the process.

2. A'thermal hydrocarbon cracking process according to claim 1 wherein the hydrocarbon feed is naphtha.

3. A process according to claim 2 wherein the aqueous solution is of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium hydroxide, or potassium hydroxide.

4. A process according to claim 3 wherein potassium carbonate is fed to the apparatus in a proportion of l to 1,000 p.p.m. of the naphtha feed.

5. A process according to claim 4 wherein the potassium carbonate is in a proportion of IO to 50 p.p.m. of the naphtha feed.

6. A catalytic dehydrogenation process for preparing butadiene according to claim I.

7. A process according to claim 6 wherein the aqueous solution is of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium hydroxide, or potassium hydroxide.

8. A process according to claim 7 wherein potassium carbonate is fed to the apparatus ina proportion of l to 1,000

p.p.m. of the hydrocarbon feed.

9. A process accordlng to claim 8 wherein the potassium carbonate is in a proportion of l0 to 50 p.p.m. of the hydrocarbon feed.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION James Ely King, Jr. Sidney Theodore Jones rson Chemical Company, Inc.

Assignors to Jeffe a corporation of Delaware Houston, Texas,

error appears in the above- It is certified that d Letters Patent are hereby identified patent and that sai corrected as shown below:

Column 3, line 2 of table, "C following "Ethylene and propylene" should be omitted; Column 3, following the table, the following sentence has been omitted Comparable results to those in the Table, supra, are obtained with the other alkali metal salts and hydroxides of our invention and in cracking units for other hydrocarbon feeds, for example, crude oil, field condensate, gas oil, kerosene, naphtha, butane and natural gasoline and in dehydrogenation units for preparing butadiene from butane or butylene.

Signed and sealed this 6th day of June 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR ROBERT GOTTSCHA LK Attesting Officer Commissioner of Patents 

2. A thermal hydrocarbon cracking process according to claim 1 wherein the hydrocarbon feed is naphtha.
 3. A process according to claim 2 wherein the aqueous solution is of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium hydroxide, or potassium hydroxide.
 4. A process according to claim 3 wherein potassium carbonate is fed to the apparatus in a proportion of 1 to 1,000 p.p.m. of the naphtha feed.
 5. A process according to claim 4 wherein the potassium carbonate is in a proportion of 10 to 50 p.p.m. of the naphtha feed.
 6. A catalytic dehydrogenation process for preparing butadiene according to claim
 1. 7. A process according to claim 6 wherein the aqueous solution is of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium hydroxide, or potassium hydroxide.
 8. A process according to claim 7 wherein potasSium carbonate is fed to the apparatus in a proportion of 1 to 1,000 p.p.m. of the hydrocarbon feed.
 9. A process according to claim 8 wherein the potassium carbonate is in a proportion of 10 to 50 p.p.m. of the hydrocarbon feed. 